I've had one of these for ages and these days couldn't do any modelling at all without them.
I find them better than the typical 'optivisor', they are lighter and much less cumbersome, so you can wear them for longer and because there is no hood, you can look over the lens to do things that don't need magnification without having to adjust them. In fact, if you position them in the right spot, with glasses you can get three different focal lengths (natural, glasses and glasses/Mageye) by moving just your head and eyes.
And believe me, with my rapidly deteriorating eyesight I need all three!
As to which magnifcation set? I have the 2&4 but I guess it depends on how far gone your eyes are, if they are just starting to go, I would go the lower set.
Cheers!
Joe Thomlinson